Paradigm in sustainability and environmental design: lighting utilization contributing to surplus-energy office buildings.
The historical approach of human centered lighting design is based on planning concepts that incorporate local climatic, environmental and cultural design principles. Such an approach is an integral component to the energy performance of a building and to the quality of space experienced by occupants. In the past, enclosures were designed to avoid negative effects on people. The forms were used to modify the intensity and distribution of daylight in order to create appropriate luminous environments. Fenestrations were designed to eliminate excessive thermal and visual solar gain that, if not controlled, would lead to occupant discomfort. The brightness and distribution of the sunlight were controlled to avoid glare.
The design of the Masdar Headquarters (MHQ), in responding to climatic context, establishes a link between the historical and modern precedents, applying innovative technologies to provide an improved environmental condition. The architectural lighting concept controls and adapts the environment for improving energy efficiency, optimizing visual comfort, maximizing visual performance, creating an aesthetically pleasing environment, and potentially en-hancing the psychological health and wellbeing of the building occupants.
Design for daylight is conceived here not as how to provide enough daylight in a space, but as the active utilization of daylight to achieve a well defined purpose. Daylighting is conceived as how to provide enough daylight without any undesirable side effects that would create an unproductive environment for building occupants. Electric lighting is optimized in relation to naturally available light based on the variability in architectural design and to enhance the indoor environmental quality of the building.
The natural environment may have significant psychological and physiological effects on health and wellbeing of humans. The literature indicates that the amount of time that humans experience outdoor spaces is increasingly limited [Frumkin 2001]. Modern society, in fact, insulates people from outdoor environmental stimuli [Stilgoe 2001; Chu and Simpson 1994]. Yet, contact with nature can result in positive human health benefits ranging from: enhancement of mental wellbeing [Kaplan and Kaplan 1989], improved social integration [Kuo and others 1998], and to the promotion of individuals' ability to deal effectively with daily life challenges. According to Kiiller and Wetterberg , the health benefits are due to daylight. Daylight contact can affect work-related stress and job satisfaction levels. Exposure to daylight for at least 3 hours a day was found to cause less stress and higher satisfaction at work. Suffering from sleep disorders, younger age, job-related health problems and educational level were found to have total or partial direct effects on occupants being exhausted [Alimoglu and Donmez 2005]. In order to optimize circadian rhythms, sufficient illuminance must be received at the eye for sufficient durations [Amp and Boubekri 2008] and at the appropriate times-of-day.
When placed in environments that create undesirable or unsuitable situations, occupants tend to reject these environments and instead seek suitable and supportive ones [Rapoport 2005]. The task of architecture is to create space where occupants can effectively communicate. The practice of utilizing natural and high-performance electric lighting in buildings provides a vehicle to the design and creation of a sustainable built environment. It also advances occupant's visual comfort and psychological wellbeing. According to Houser and Tiller , an understanding of shared lighting preferences is of considerable importance to lighting design. To them, for the professional practice of lighting to grow and mature, it must progress from qualitative guidelines to quantitative procedures. Mardaljevic and others , realize that daylight metrics founded on climate-based simulations have begun to be considered as the basis for the next generation of building guidelines. Beyond the visual effect of light, there has been a gradual increase in awareness of the nonvisual effects of daylight received by the eye [Webb 2006]. Light has been identified as a stimulant and has direct alerting effects in the brain including measurable effects on subjective sleepiness ratings, reaction time and cognitive performance and brain activity [Lockley 2009]. There is a notion that a space, through its interaction with daylight, may possess a certain circadian potential [Pechacek and others 2008].
The purpose of this paper is to document and highlight several lighting design strategies that are part of the MHQ design philosophy. It also examines the various components of the visual environment in an attempt to identify the importance of these components in achieving a net-positive energy building.
3 BUILDING DESCRIPTION
The MHQ is a mixed-use, large scale positive energy building located within Abu Dhabi's Masdar City. The Masdar Initiative is the bold vision of Abu Dhabi as the first major hydrocarbon-producing economy to transform itself into a global leader in new sustainable energy through the Abu Dhabi Future Energy Company (ADFEC). In 2008, ADFEC announced the first prize in a global design competition for the Masdar Headquarters building, which was selected for construction at the heart of Masdar city. Adrian Smith + Gordon Gill Architecture LLP secured the first prize along with other systems engineering firms.
The approach that led to the winning design considered a systemic evaluation of the whole building structure and systems, environmental context, and economic objectives for ADFEC by a cross-disciplinary integrated design team. Both passive and active strategies were identified to maximize building performance and to embolden the building as a future icon of energy sustainability in the built environment, most notably the eleven conical towers and the long span trellis they support. A unique aspect of the design process was the establishment of specific measurable targets, or key performance indicators (KPIs) early within the design process to ensure the resulting building embodied the comprehensive objectives for project sustainability and performance. The facility is a five-story above podium-level building with 56 percent offices, 6 percent retail and food amenities, 24 percent circulation, and 15 percent storage/MEP areas. With the ground level floor, the total area of the building is 114,000 m2.
For the MHQ, a comprehensive climate analysis at the onset of the design process was critical to engendering an integrated architecture and building system solution to minimize energy consumption and maximize occupant comfort. A summary of the climate conditions likely to be experienced is identified by Abu Dhabi's location along the coast of the gulf at 24[degrees]28' N latitude and 54[degrees]22' E longitude within an intense climate classified as a subtropical hot desert. The climate is characterized by high humidity in summer due to a trade wind pattern that draws wind across the hot Saudi Arabian desert prior to crossing the gulf subsequently increasing absolute humidity leading to a summer design condition with a 47.3[degrees]C extreme dry bulb temperature and a 33.8[degrees]C extreme wet bulb temperature. This high level of humidity also serves to dampen diurnal temperature fluctuations, reducing the efficacy of energy saving strategies such as nighttime purge ventilation or thermal mass. Winter months are mild with a minimum design temperature of 8.4[degrees]C and are relatively arid with cooler winds approaching from the south or east. Rainfall is sporadic, though potentially heavy, with annual average of 80-100 mm, mostly occurring within winter months. Further details pertaining to climate analysis for the MHQ can be found in Boyer and others .
In this context, the design team, including the authors, focused on introducing a complex that integrates historically successful building strategies for climate responsive architecture in conjunction with the latest technology and innovative building systems. The design includes numerous systems that generate a surplus of the building's energy demand, thus offsetting carbon emissions while also dramatically reducing solid waste and waste water. Daylighting design strategies and electric lighting concepts also present the ideal integration of architecture and engineering, resulting in a dynamic, inviting building. The roof canopy, cones, and sawtooth exterior walls are design features that directly contributed to the form and performance of the building. They are illustrated in Figure 1 and are summarized in the sections that follow.
[FIGURE 1 OMITTED]
3.1 ROOF CANOPY
The large roof canopy integrates roof mounted solar energy arrays. It also provides a shaded microclimate and protection from the harsh desert climate while allowing air to circulate beneath and through the system. Diffuse sunlight is admitted to the lower plaza and green habitable roofs, with paving and water features acting as ecological buffer at the roof top of the building.
Eleven conical support towers extend from the trellis down to the podium level.
These multifaceted structures have a variety of functions: 1) act as wind towers (one of the building's references to traditional Islamic architecture) exhausting warm air, ventilating the building, as well as bringing cool air up through the subterranean levels of the city below; 2) admit daylight throughout the building by serving as internal courtyard, another traditional concept; 3) act as structural support to the building's canopy and integrated photovoltaic panels; and 4) create garden courtyards at the public realm which have pools of light and water providing amenities and public space for occupants.
SAWTOOTH EXTERIOR WALL The facade consists of a unitized aluminum thermally broken frame curtain wall system horizontally faceted on a 1.5 m module. The vision glazing faces due south/north, and the nonvision glazing faces due east/west. This configuration is considered in order to meet the following design criteria: 1) access to daylight and views through transparency and connection; 2) mitigate glare induced visual comfort; 3) minimize solar heat gain; 4) mitigate reflectance on adjacent buildings; 5) provide transparent heat insulation and thermal mass; and 6) offer structural economy.
3.4 INTEGRATED LIGHTING SYSTEM
The design integrates energy efficient lighting technologies, fittings, and controls specifically designed for the varying natural lighting conditions and building program, including: 1) a limited number of light fittings to improve life cycle costs, reduce operating costs, and support the long term peak performance of the system; 2) distributed digital controls to create a tunable lighting system that can maximize energy efficiency and system flexibility; and 3) white light with high color rendition including ceramic metal halide (CMH), fluorescent, inductive fluorescent (QL), and LED.
4 NATURAL LIGHTING DESIGN
Daylight is dynamic and changes constantly according to hours, days, and seasons. Some of its qualities include variable color, intensity, and angle, which create dynamic connections with the outside world. The building envelope provides a means of contact with the outdoors and serves to filter this connection between people and the external environment. Good daylighting design starts with an understanding of the relationship between the building form and the position of the sun through the sky and seasons. Careful envelope design can maximize available daylight, bringing diffuse natural light into the building as far as possible, while shading and spectrally-selective glazing can minimize glare and solar heat gain.
Recent new approaches and tools have been proposed in order to provide an alternative methodology to using discrete dates and times that designers usually use to evaluate daylight performance in buildings [Leslie and others 2011]. Many of these approaches recommend using simulation software [Mardaljevic and others 2009, 2011; Araji and Boubekri 2011; Reinhart and others 2011; Cantin and Dubois 2011] while another recommends the use of rule-of-thumb sequences [Reinhart and LoVerso 2010] to simplify the decision-making process during conceptual design. The downside of these approaches lies in their complexity [Mardaljevic and others 2009, 2011; Reinhart and others 2011; Cantin and Dubois 2011] or conversely, in overly simplified assumptions [Reinhart and LoVerso 2010]. In this study, daylight availability was predicted using parameters such as daylight factor, daily radiant energy, and sunlight patterns. Three days were analyzed: June 21, September 21, and December 21. Using Abu Dhabi climate data, simulation analysis was conducted for the basic geometry of the cones, fenestration wall, and garden courtyard beneath the roof canopy.
The cone design was analyzed by exploring daylight availability relative to the diameter of the upper oculus at the trellis level. The basecase scenario assumed that the upper oculus diameter of the cone would be 11 m, and the conceived scenario considers an oculus diameter of 33 m. This experiment was built upon the hypothesis that increasing the oculus diameter would yield substantive increase in daylighting to perimeter office areas and to the base of the cone. This, in turn, could expand the daylit zone at each floor, improve direct sunlight penetration for garden courtyards at the roof and ground level, and enhance the overall ground level illumination that could potentially improve the experience of building occupants.
A computer simulation of the cone was used to perform the analysis. The model is based upon representative geometry of the cone and features the following characteristics: 1) the cone is visualized in a nonreflective (black) enclosure to confine the daylight contribution to the oculus of the cone; 2) no additional light sources are introduced to influence the space for this study; and 3) general reflectance and light transmission values are assumed as follows: floor reflectance = 20 percent, ceiling reflectance = 80 percent, cone glass transmittance = 70 percent, and roof glass transmittance = 50 percent.
4.1.1 DAYLIGHT FACTOR
Preliminary results showed that the daylighting contribution of the cone to the perimeter office areas gradually drops-off as it penetrates to interior spaces, with the exception of the top floor and in the atrium space at the base of the cone (Fig. 2). The intervening floor plates have small areas of daylit space (DF > 2 percent) within 5 m of the cone perimeter. The light levels drop beyond this area, resulting in a relatively darker floor plate with a bright central view. Thus, supplemental electric lighting will be required in offices to balance brightness perception. In this basic configuration, the cone will essentially be a glowing lantern; its brightness will be offset with electric lighting deeper in the floor plate to achieve visual comfort. It's important to mention that the major factor affecting discomfort glare sensation is high source luminance [Chauvel and others 1982; Chauvel and Perraudeau 1995; Nazzal and Oki 2007]. Luminance in the visual field that surrounds a task can have different effects on visual ability depending upon the areas involved, their location with respect to the line of sight, and their actual luminances as compared with that of the task. To limit transient adaptation and discomfort glare, it's suggested that the current study needs to be supplemented by luminance ratio analysis to confirm whether or not results are within the the recommendations of IES [IES 1993] or the British equivalent CIBSE . Overall, both models (that is, large and small apertures) yield similar results, showing that a larger daylight opening does not significantly expand the daylit zone of each floor; however the larger oculus would lead to increased heat gain and therefore was rejected as a design solution.
[FIGURE 2 OMITTED]
Another finding of this analysis was related to the relationship between ground level albedo and daylight availability. As a result of the the concave form of the conical geometry, a significant amount of daylight is introduced into the offices indirectly through reflectance off the podium level. An albedo of 55 percent was found to provide an optimal balance between the intensity of light and the reflected component used for uniform luminance distribution across these spaces.
4.1.2 DIRECT SUN PENETRATION
Although direct sunlight will create high contrast and a potential for glare, this light does not penetrate very deeply into the floor plates beyond the cone perimeter (Fig. 3). With the small aperture, direct sunlight passing through the oculus only penetrates far enough to fall on the ground floor at the base of the cone for approximately 5 months of the year. With the larger aperture studied, direct sunlight would fall on the ground floor for approximately 7 months. During these months, significant areas of the ground floor are illuminated for 3-5 hours per day. The landscaping at the base of the cone will be predominantly illuminated with indirect light reflected by the upper portions of the cone. Maximum direct sunlight hours are summarized in Fig. 4.
[FIGURE 3 OMITTED]
Fig. 4. Period of direct sun penetration falling at the cone base. Top Significant Months Maximum Time of Oculus Months/Year of the Hours/Day(Hr) the Day Diameter (Month) year of the Cone Small 5 Apr-Aug 3 11am-2pm aperture Large 7 Mar-Sep 5 10am-3pm aperture
4.1.3 GROUND LEVEL ILLUMINANCE
This study tracks the amount of energy from the sun reaching ground level at the base of the cone (Fig. 5). It measures photosynthetically active radiation (PAR), a measure of light falling on a surface that is within the spectrum which is useful to plants in the process of photosynthesis (400-700 nm). Values are expressed as Watt-hours per square meter (Wh/m2) and represent the daily average (total throughout the study period divided by number of days). There are two time periods considered for analysis here: March 22-September 21 (summer), and September 22-March 21 (winter). The study also measures the average daily total (ADT) showing the total amount of energy from the sun and sky reaching the base of the cone (full spectrum) on an average day.
Analysis was performed on the small aperture only as it was hypothesized to provide sufficient PAR and ADT. Results show that winter values are more evenly distributed because primary illumination comes from sky light (direct sun does not reach the base of the cone between September and March), while summer values are highly concentrated in the northern area due to direct sun contribution between March and September. Values are summarized in Fig. 6.
Depending on the plant species and other growth factors, each plant shows a minimal need of light for growth and a light saturation point at which photosynthesis stagnates. Plants can be divided into different categories depending on their light requirements. Species with low light requirements only need 2 W/[m.sup.2] (PAR), with medium 4 W/[m.sup.2] (PAR), and high 6-8 W/[m.sup.2] (PAR). Only few plants need 10-20 W/[m.sup.2] (PAR). Overall, the results in Fig. 6 (with 183 days for each period) show that enough PAR is available to support plant growth at the base of the cones. Specific species are identified for the project include benjamina, linearis, microcarpo nitido, lyrata for deciduous and ornamental trees; subulata and tenuifolia for ground covers; and ficoidea, lyrata, nigrum, ocaulis for perennials.
[FIGURE 5 OMITTED]
Fig. 6. PAR and ADT reaching the cone base. Period PAR(W/h ADT(W/h [m.sup.2]) [m.suop.2]) At Perimeter At At Perimeter At Center Center Summer 0.01 0.85 6.65 584.74 Winter 0.004 0.05 2.58 30.24
4.2 OPEN COURTYARD
The open courtyard is located beneath the roof trellis at level four. The surface provided by the trellis serves to support a photovoltaic array, which comprises rows of two modules stacked end-to-end in a uniform pattern. All modules are oriented with a 180 degree azimuth (due south). Of the two stacked modules, a combination of 5[degrees] and 15[degrees] slope was used to maximize PV surface and overall system output while maintaining uniform daylight transparency. To preclude shade created by the PV module tilt from adversely affecting the adjacent module row, the module rows are spaced 593 mm apart. The separation distance also serves as a walkway for PV module cleaning and maintenance. This configuration was based on optimization of the trellis PV panel arrangement.
To that end, the modeled space below consists of the courtyard with peripheral geometry, and includes shading from PV panels affixed to the trellis. The trellis and the surrounding levels of the building have the most impact in shading the courtyard, while daylight is introduced from the cones and internal spaces between the roof and upper floors. Below we present the daylight factor and the daily total radiant energy of the courtyard space.
4.2.1 DAYLIGHT FACTOR
The DF ranges from 10 to 32 percent with an average of 19 percent. Based upon latitude, the design sky value for Abu Dhabi, UAE is 9200 N. Thus, a space of DF 19 percent should be receiving 1748 lx from a clear sky, with no direct sun. This value (1748 lx) is based on design sky, which is the 15th percentile sky value. This means light levels will be less than 1748 lx for 15 percent of the year (8 weeks), and more than 1748 lx for 85 percent of the year (44 weeks). This translates to lower light levels from the clear sky will likely occur from mid-Nov to mid-Jan. It is worth mentioning that design sky values are averaged values (that is, these numbers are not absolute, they are a baseline that will likely have great deviation throughout the day and year).
The lux values (Fig. 7) for Jun 21 represent the maximum daily average of the year. Areas in the direct sun path receive illumination in the range of 8500 to 400001x. All other areas (outside direct sun path) receive diffuse illumination in the range of 850 to 2850 lx. Additional bright spots are created by reflections of the cone glass, around 85001x. The lux values for Sep 21 are similar to those of Jun 21 because of effects of direct sun in the space. Illumination ranges from 8500 to 45500 lx in the direct sun path and 850 to 2850 lx for other areas with diffuse illumination. The lux values for Dec 21 represent the minimum daily average for the year. Areas in the direct sun path receive illumination in the range of 9900 to 19900 lx. All other areas receive diffuse illumination in the range of 1400 to 5700 lx.
4.3 EXTERIOR WINDOW WALL
The building envelope is the critical path between the internal environment that the authors wish to control, and its ever dynamic and potentially extreme external counterpart. As a result, it was one of the most important elements of the building design. Among several window wall typologies tested throughout the design process, two exterior envelopes are analyzed for their daylighting characteristics in this paper. The first represents a flush facade with vertical external louvers and the second represents an oriented scheme facade with sawtooth like geometry whereby vision glazing faces due south/north and nonvision glazing faces due east/west. Both typologies are horizontally faceted on a 1.5m panel module and represented by 30 percent vision glass, 60 percent insulated spandrel, and 10 percent mullion.
[FIGURE 7 OMITTED]
The digital model utilized for simulation incorporates the following characteristics: 1) the module is represented by a 9 m x 9 m section of building perimeter, 2) nonreflective surrounding walls were used to ensure that only light contribution from glazing affects DF and direct sun penetration calculations, and 3) floor and ceiling reflectances were considered to be 20 percent and 80 percent, respectively. The visible transmittances of the vertical louvers and sawtooth models were set at 50 percent and 30 percent, respectively (Fig. 8).
4.3.1 DAYLIGHT FACTOR
Daylit area (DF > 2 percent) extends 5 to 6 m into the space with Sawtooth, and extends 4 to 5 m into the space with vertical louvers (Fig. 9). This difference is mainly due to the height, glazing orientation, and the visible light transmittance percentages. Both models have a DF of 15 percent near the window glazing. Typical areas not in the daylit zone benefit from additional daylight apertures like cones, light wells and light filtration through the upper shading canopy which help to alleviate the daylight levels across the lease span in addition to electric lighting. Lease span refers to the depth of useable space between the exterior wall and the building core. This space has a potential for the use of daylight.
Fig. 10. Period of direct sun penetration for exterior vertical louvers and sawtooth wall systems. Facade Model Maximum Significant Sunlight Orientation Type Hours/Day Months/Year Patterns (Hr) (Month) North-West Sawtooth 2 3 Larger Vertical 3 6 Smaller Louvers North-East Sawtooth 2 1 Larger Vertical 4 5 Smaller Louvers South-East Sawtooth 6 5 Significant Vertical 5 12 Significant Louvers West ISawtooth 5 12 Significant Vertical 5 12 Significant Louvers *Smaller = best and Significant = worst
4.3.2 DIRECT SUN PENETRATION
Each model was tested using four orientations: northwest, northeast, southeast, and west. These correspond to the four primary orientations of the exterior facades. The studies used to make the most of the given siting and orientation.
Overall, the sawtooth performs slightly better in both the daylight factor and direct sun penetration analyses (Fig. 10). It was also noticed that some design modifications can be applied to either model to improve performance. These include: 1) a large area of glazing and a higher VLT percentage result in more diffuse illumination; 2) a higher head-height (top) of the glazing allows daylight to reach further into the space; 3) vertical shading devices oriented exactly to the angle of the site (for example, 38[degrees] instead of 45[degrees]) result in slightly better shading of direct sun throughout the year; and 4) a smaller module of the window-shade unit allows for better shading of direct sun (ratio of window size to shade size approaching 1:1, as in sawtooth type).
5 ELECTRIC LIGHTING DESIGN
Electric lighting has significant impact on the environment because it is one of the major energy end-uses in buildings. The production of electricity needed for lighting consumes fossil fuels, which contribute to air and water pollution. Besides, lifecycle assessment shows the environmental costs from project inception to disposal of lighting equipment and components. This, in turn, creates a continuous waste stream. Raw materials are first extracted or harvested from the earth, delivered to manufacturing, installed as light fittings in buildings, and finally disposed.
While natural light is highly desirable and an essential part of the MHQ sustainable design program, it must be supplemented by electric lighting. Thus, an effectively integrated balance of daylighting and electrical lighting is an important goal and a significant technical challenge. In this context, several daylighting strategies have been studied and proposed in order to reduce electrical lighting energy demands [Mardaljevic and others 2009; Doulos and others 2008; Yun and others 2011].
On the whole, light sources should offer the highest efficacy and longest lamp life appropriate for each use. Fittings must feature high performance optical systems as well as robust construction to meet the demands of the environment. The lighting control system should be a comprehensive, scalable, unified system consisting of microprocessor based lighting controls, dimming ballasts, power cabinets, and human interface stations networked to master control software located in the building management office. Such design approach serves to maximize energy efficiency, minimize maintenance, and provide the best long-term sustainability.
The permanent consideration for lighting design is achieving a visually comfortable environment with lowest possible energy demand. Proper light distribution creates a more stimulating environment that doesn't represent a potential case for physiological pain [Steffy 2002], distraction, and potentially harmful conditions [Rea 2000; Araji and others 2007]. The Illuminating Engineering Society indicates that among the more common and extensive list of symptoms associated with visual discomfort are red, sore, itchy, and watering eyes; headaches and migraine attacks, gastrointestinal problems; aches and pains [Rea 2000]. Overall, optimizing the visual properties of the indoor environment is the major goal for attaining visual comfort.
The following provides a brief qualitative and quantitative documentation of the concepts used to specify the basis of the electric lighting system for the MHQ. This system is serving as the seamless integration of passive design, which relies on dynamic play of active lighting technologies to realize positive energy building. It is intended here to focus on the lighting program specifics and lighting controls strategies.
5.1 LIGHTING PROGRAM SPECIFICS
A unique aspect of the design process was the establishment of specific measurable targets early within the design process to ensure the resulting building embodies the comprehensive objectives for sustainability and performance. These delineated targets influence the design, selection and operational dimensions of the electric lighting system. Major components of the program include:
5.1.1 MATERIALS SELECTION
The careful selection of building materials is a critical component of a sustainable design. Materials decision-making requires adherence to the requirements of the MHQ restricted materials list which is mandatory for all temporary and permanent projects of the Masdar development program. Mercury in lamps is considered a challenge. As a result, LED lighting is used extensively throughout the building where it is most appropriate. Generally, these include curvilinear applications where linear fluorescent lamps cannot be used or where low-level target illuminance is required. For general area lighting, fluorescent lighting is most appropriate since it is at least twice as efficient as commercially available LED light fitting equipment. It would not be realistically possible to effectively light the building with LED technology alone while still meeting requisite energy requirements. Unfortunately, fluorescent lighting does require mercury to function. To that end, a comprehensive fluorescent lamp recycling program was introduced to recover mercury from the lamps. It is important to further note that attempting to use LED light sources as general area illumination would violate the 80 lumens per watt light source requirement of the facility.
Other restricted materials (that are directly applicable to lighting design and) were considered for elimination from being used in the building include metals such as chrome, copper (virgin), aluminum (virgin), and lead; and chemicals like PVC in the case of wiring and cable insulation.
5.1.2 LIGHTING POWER DENSITY (LPD)
Office spaces comprise the largest program allocation of the MHQ at 55 percent of building area. An indirect/direct lighting system was adopted in these spaces to optimize visual comfort, maximize visual performance, balance available daylight, improve energy efficiency, offer maintenance simplicity, and enhance psychological wellbeing of space occupants. The target for lighting power density (LPD) was set at 5.6 W/[m.sup.2] which provided improvement in energy performance compared to the master plan of the Masdar City guidelines. This number is assumed across the usable areas based on approximately 75 percent of the space being an open office layout. The private office/conference and circulation spaces represent 10 percent and 15 percent of total office area, respectively. Figure 11 lists the LPD of the interior lighting system. The total annual consumption for exterior lighting was estimated at approximately 148,241 kWh. This is applied at the podium accessible areas, cones (at all floor levels), and roof garden. Indoor lighting consumption is anticipated at 1,108,500 kWh.
Placing light where and when it is needed emphasizes the high quality of its usage. This precision approach to the lighting system reduces wasted light and electricity use. The dynamic balancing of natural and electric light also generally lowers electric light levels. Further critical human factors in the design of the lighting system are considered. The elimination of visual noise (that is, light trespass, light pollution, and uncontrolled spill light) was coordinated, and light was integrated into the architectural plan and graphics to clarify and support building-wide wayfinding.
Fig. 11. Interior LPD. Space LPD (W/[m.sup.2]) Office 5.64 Task lights 0.76 MEP Spaces 4.00 Storage 4.00 Non-Office Circulation Space 5.50 General Employee Space 10.40 Restrooms 10.00 Retail Tenants 8.00 Food Amenities I 9.50 Fig. 12. Summary of ambient-lighting horizontal illuminance in office-related areas. Space Avg Max Min Avg/ Max/ (Lux) (Lux) (Lux) Min Min Open office 223 515 2 104 240 Open office 134 309 1 125 287 dimmed to 60% output Private 172 340 28 6 12 office Small 182 347 24 8 15 conference room Large 297 646 62 5 10 conference room 1
Benefiting from brightness perception provided by lighted surfaces allow to save energy through using a task/ambient lighting strategy. This strategy permits the adoption of a lower relative ambient light level provided over large areas while higher light levels are targeted to specific task areas as required. Furniture and adjustable task light luminaires are assumed for each workstation. These include a 9-watt LED shielded task strip mounted to the furniture system and a 6-watt LED moveable luminaire. The expected illuminance from both task lights is about 519 lx. To maximize energy performance and preserve daylight views, interior finishes and furnishings were designed with light finishes and partition heights were constrained. Figure 12 presents the illuminance summary for office spaces.
Fig.13. References to lighting control energy savings. Control EO-LBNL ALG NCAR NYT Strategy Private Private Open Private General Single 0% 0% 0% 0% 0% Level Switching Scheduling - - - - 1.4% Bi-Level 23% 30% - - - Switching Dimming - 23% 30% - 6% 40.6% Task Tuning Photo 27% 35% 40% - 21% Sensors Occupancy 20-26% 45% 35% 43% 7% Sensors Occupancy 29% - - 61%* - Sensor + Manual Dimming Occupancy 43% - - 61%* - Sensor + Task Tuning Occupancy + 46% - - 61%* - Photo Sensors Reference/Casestudy - EO-LBNL: Ernest Orlando LBNL (Jennings et al, 1999), ALG: Advanced Lighting Guidelines (NBI, 2011), NCAR: National Center for Atmospheric Research (LRC, 1999), NYT: New York Times Building (Lutron, 2008). *Energy savings from combination of manual and automatic controls.
5.2 LIGHTING CONTROLS
Advanced high performance lighting controls are critical to achieving the building's energy and sustainability goals. Lighting is one of the largest energy consumers in buildings [Nicol and others 2006] and could account for 5-15 percent of the total electric energy consumption [Ryckaert and others 2010]. Lighting controls in connection to daylighting can save 20-40 percent of lighting energy [Yun and others, 2012]. Other references to energy savings estimates from lighting control strategies are shown in Fig. 13. Dubois and Blomsterberg  published a literature review on additional energy saving potential and strategies for electric lighting in low energy office buildings. The review indicates that an energy intensity of around 10 kWh/[m.sup.2]yr is a realistic target for office electric lighting in future low energy office buildings. To Dubois and Blomsterberg, this target would yield a significant reduction in energy intensity of at least 50 percent compared to the actual average electricity use for lighting.
Fig. 14. Lighting control strategies in office buildings. Space Type ATC TC DS OS PS TT LS TD Application 0% Score 100% Office * * * * * * Conference * * * * Retail * * * Exhibition / * * * * Cone Toilet/Storage * Corridors * * * Circulation * * * * Roof Gardens * * Exterior * * Lighting ATC: Astronomic Time Clock, TC: Time Clock, DS: Daylight Sensor, OS: Occupancy Sensor, PS: Preset Scene, TT: Task Tuning, LS: Load Shed, TD: Theatrical DMX-512. * The Application Score indicates the possible number of lighting control strategies applications relating to various spaces in an office building.
With the MHQ, the concepts of the lighting controls are based on maintaining four guiding principles to inform the system design, including energy effectiveness, ease of installation, maintainability, and cost efficiency. Specific characteristics of the lighting controls carry the principles:
* Designing comprehensive, scalable, unified system consisting of microprocessor based lighting controls, intelligent fluorescent digital dimming ballasts, dimming and relay panels, automated interface devices, and human interface stations networked to master control software and equipment.
* Allowing building managers to log energy use over time, real time energy use, individual space occupancy, and facilitate operational scheduling for tasks such as group relamping cycles. Supporting operational load energy savings through daylight harvesting, occupancy based dimming and switching, time of day automated controls, wide area task tuning, individual office task tuning, and wide area load shed capabilities when required.
* Specific lighting control strategies employed for the MHQ are summarized in Fig. 14, including:
- Astronomic Timeclock Scheduling: Time of day events in large scale public areas with daylight availability are keyed to sunrise and sunset calculated daily according to project latitude and longitude; respectively 24[degrees]28'N and 54[degrees]22'E.
- Timeclock Scheduling: Time of day events in large scale office areas are keyed to project programming requirements. Several schedules are used to accommodate weekday, weekend, and holiday schedules. Over-ride wall stations are provided in appropriate locations to allow timed over-ride of office "sweeps" to off for use during atypical times.
- Daylight Sensor Dimming: Light fittings in perimeter and interior daylight zones on office floors are governed in groups by photosensors determining real time daylight availability within each area. Fluorescent light fittings are dimmed (by digital ballasts) accordingly when daylight is present.
- Occupancy Sensing: Almost all spaces on the office floor levels of the building will be controlled by occupancy sensors. Enclosed spaces such as private offices, conference rooms, toilet rooms, and storage rooms will function as manual touch on spaces with occupancy sensors extinguishing lights after a 15 minute interval with no detectable occupancy. Open plan office areas are to be provided with one occupancy sensor per approximately 70 [m.sup.2] of occupied space. Occupancy sensors in open plan areas will dim unoccupied areas to 30 percent light output after a 15 minute interval with no detectable occupancy. The lighting in these areas will all be turned off via timeclock after hours with an override switch for any afterhours use.
-Task Tuning: Dimming allows for fine tuning of lighting systems to acceptable specific user performances for specific tasks and adjustment of large areas to maximize energy savings.
- Preset Scene Controls: Allows for programming preset scenes for flexibility, repeatability, and fine tuning of light levels in specific spaces.
- Load Shedding: The lighting control system is configured to take real time signals from the BMS system to dim fluorescent lighting over large areas to shed load if required during unusual or peak demand times.
- High efficiency theatrical control (via Digital MultipleX (DMX)-512 protocol and plug in portable control stations) is also part of the exhibition spaces and cones lighting design.
This advanced lighting control system is anticipated to reduce lighting energy requirements by 35 to 45 percent.
The intent of this paper was to address the lighting design approach including simulation process, technology specification, and anticipated energy performance necessary to realize the 103 percent net-positive energy goal of the Masdar Headquarters. Ultimately, a comprehensive energy estimate of the building's lighting design was used to validate this target. The building achieves the positive energy use first through passive means such as external building shading, the introduction of interior light courts to enhance daylighting effectiveness, natural ventilation strategies of the ground plane, and the incorporation of a highly efficient envelope design; and secondly through the incorporation of highly-efficient building systems and a large photovoltaic energy producing array integrated into the building shading trellis system.
Daylight harvesting was a critical component to reducing building energy consumption as well as improving the work environment and experience in the MHQ. Prescribing to the constraints of the master plan necessitated a solution to bring daylight within the large building floor plan. By introducing courtyards throughout the plan, the total building energy consumption was reduced by approximately 10 percent (or 583,150 kWh). Analysis of the daylight admission via the glazed wind towers shows its extension of 6 m into the space (with a Daylit area of DF > 2 percent). The sawtooth fenestration system was developed dependent on orientation in response to the building context. While this geometric manipulation increased the total surface area of the facade (thus increasing conductive gains), it also served to significantly reduce solar loads and the potential for glare, promoting more natural light to be utilized by the building. This morphology allowed for the east and west facing glass modules to be integrated with mono-crystalline photovoltaic cells and a highly insulated panel to minimize heat gain. It is anticipated that this system will contribute approximately 2 percent of the building energy requirements (or 122,688 kWh). Integration of the photovoltaic modules within the trellis system allowed for several unique opportunities as well. An immediate advantage is that long runs of power distribution infrastructure necessary for a remote installation are eliminated. The shade provided by the trellis reduces direct solar gains on the facade from high altitude sun and ambient temperatures experienced on the roof and surrounding areas. Temperature and daylight for the roof garden were carefully balanced against energy production when determining the spacing and tilt of the modules.
Integration of efficient lighting system in the MHQ is essential for engendering its positive energy target. The design required a concerted effort to adapting the architecture and building systems to the local climate and determining opportunities for systems integration, which create balance between human centered design and effective economic consequences. The lighting system associated with each functional area is represented with their associated operational requirements. Except for retail areas, the design was modeled with a continuous dimming system, which will dim the lights to 10 percent of maximum power if the minimum lighting level is being achieved.
In conclusion, the paper communicates and calls attention to issues regarding better support of sustainable design strategies in the architecture design process. It focuses on the knowledge developed in the course of a design project whereby patterns can be extracted, modified, and afterwards implemented in its proper manner. The designer can use the data on lighting analysis as the baseline to create numerous solutions, as design variations are endless.
It is further important to note that the building is currently under construction. As such, this paper is considered as an introductory publication to be followed by one that describes the performance of the actual building, which will include post occupancy evaluation and real data with evidence of its performance.
The authors delightedly acknowledge the tremendous efforts of the Masder Headquarters design team at Adrian Smith + Gordon Gill Architecture LLP and other involved systems engineering firms. Appreciation is extended to the Abu Dhabi Future Energy Company (Masdar). All valuable contributions are acknowledged with great thanks.
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(1) Environmental Design Program, Faculty of Architecture, The University of Manitoba, Winnipeg MB Canada, (2) Affiliated Engineers Inc., Seattle WA, USA, (3) Adrian Smith + Gordon Gill Architecture LLP, Chicago IL, USA.
*Corresponding author: Mohamad T. Araji, Email: firstname.lastname@example.org
Mohamad T. Araji PhD (1)* Shaun P. Darragh (2), and Jeffrey L. Boyer (3)
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|Author:||Araji, Mohamad T.; Darragh, Shaun P.; Boyer, Jeffrey L.|
|Date:||Jul 1, 2012|
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